[Bug sanitizer/59331] New: ubsan gives extra warnings with vla.

[larsbj at gullik dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59331

            Bug ID: 59331
           Summary: ubsan gives extra warnings with vla.
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: larsbj at gullik dot net
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org

g++ (GCC) 4.9.0 20131128 (experimental)
Copyright (C) 2013 Free Software Foundation, Inc.
r205479

This snippet:

---------
void foo(int i)
{
    char a[i];
    (void)a;
}
---------

Compiled with: g++ -c -std=gnu++11 -Wall -fsanitize=undefined

gives this warning:

In function ‘void foo(int)’:
3:13: warning: value computed is not used [-Wunused-value]

If -fsanitize=undefined is removed, no warning is given.